1. Field of the Invention
This invention relates to a magnetic bubble device for utilizing magnetic bubbles (cylindrical magnetic domains) formed in a thin magnetic film having uniaxial anisotropy, and more particularly to a magnetic bubble information writing device which generates magnetic bubbles.
2. Description of the Prior Art
Customarily is used a well-known method called the field access method in which a pattern of thin film of soft ferromagnetic material such as permalloy is formed as a circuit to propagate magnetic bubbles therethrough on the thin magnetic film having uniaxial anisotropy and in which the pattern is magnetized by a rotating magnetic field rotating in the plane of the pattern. As such a pattern have been reported a T-Bar pattern, a chevron pattern and various other types of patterns. The magnetic bubble device requires, in addition to the above mentioned rotating magnetic field, another magnetic field perpendicular to the thin, uniaxially anisotropic magnetic film. This perpendicular field is called the bias magnetic field, necessary for stabilizing the existence of the generated magnetic bubbles.
The most favorable type of the conventional magnetic bubble information writing device is the field nucleation type in which magnetic bubbles are generated through nucleation caused by sending pulse current through a hairpin-shaped conductor loop disposed on a magnetic bubble propagation circuit. When a pulse current is sent through the conductor loop in such a direction as to decrease the intensity of the bias magnetic field, a magnetic bubble is created inside the loop of the conductor. The thus created magnetic bubble is propagated along the propagation circuit as the rotating magnetic field rotates. By sending and interrupting such a pulse current in accordance with the information "1" or "0", the information pattern "1" or "0" can be written in the magnetic bubble propagation circuit.
The conventional magnetic bubble information writing device described above has the following problem. Namely, if magnetic bubbles are generated repeatedly for a long time in the region of the magnetic film where the intensity of the bias magnetic field is low, an erroneous operation will be caused, that is, a great number of undesirable, unwanted magnetic bubbles (hereinafter referred to as stray bubbles) are generated in the region of the thin magnetic film inside the conductor loop. As the repulsive force among the stray bubbles increases with the increase in the concentration of the stray bubbles, some of the stray bubbles intrude into the propagation circuit to destroy the useful information stored in the circuit. In order to eliminate such an erroneous operation, a bias magnetic field must be used which has an intensity higher than a certain threshold value and in that case the margin of the bias magnetic field is very narrow.